I'm curious as to why the tank level makes a difference. In theory, once the tank contains some liquid, it will be at the same pressure regardless of the level. Does the tank get excessively cold after a run on LPG?

This is the bit that I cant get my head around either, as you say pressure should be the same untill your running on fumes, and then it should cut out, which it does as per any other LPG system Ive driven.

So for me, 2 things, Level Sender or Temperature, for now Ive ruled the Tank Level sending, as it pretty much does what it says on the tin. Full Tank, half Full, Empty etc all fine (apart from Vauxhalls stupid "One fuel gauge does Both", which can take up to 10 mins to show the contents between Petrol and LPG on the same gauge, depending what position the LPG switch is, but thats normal).

With reference to the above replies, its probably also worth pointing out that the Flashing Green LED has 3 modes when its in the LPG ON position, Slow Flash = all Normal, running on Petrol, waiting for LPG to kick in, No Flash = running on LPG, Fast Flash = There's an Issue, Forced back to Petrol. Now, the only time it Fast Flashes, is when the Tank is Empty / Run Out and and its forced back to Petrol, ie, the issue is you've run out of Gas, all other times when it reverts back to Petrol as per the issue, the LED flashes normal, which also kind of confirms to me, that its not a Tank Sender issue or has thrown a Fault. Obviously if I tamper with it whilst on LPG, ie, unplug something, like Temp or Vacuum Pipe Sender it will revert back to Petrol and Fast Flash but that is only to be expected.

So Temperature, does a Full tank of LPG compared to a near Empty one deliver LPG to the Vap at a colder temperature, in theory no, in practice?, Im not clear on this, if does and the Vap is just about doing a catch up with its heat then that does kind of explain the issue.

Well, the coolant has made a difference, so that's a clue, in my book. Might be worth checking out how to clean the "heavy ends" out of the vapouriser, as it's possible that could affect its efficiency, making it over critical on coolant.

Ok, on the List, but why is it running perfect with half a Tank or less.

Also, worth jumping out and checking the vapouriser temperature when it switches back to petrol. If the vapouriser freezes up, the coolant passages will start to block, and it's a vicious circle.

Ive already checked this, the Vap runs from warm to cooler when switching back to Petrol, Not freezing, but cooler sometimes with some condensation present on the body after a run, should these things be hot, if so how hot?

Does it tend to switch back to petrol when under lots of load or when idling, or both?

Doesnt seem to make a lot of difference whether causally ploding along or flooring it, you kind of get a fill for it on distance, its almost like, after a mile or so you think its going to switck back to petrol now, and iy does.

If you park up with the engine running it will run all day long on LPG until you start to drive again, but I would expect this to be the case even under extreme cold weather, warm static engine bay compared to the chill factor when moving.

From the behaviour of the LED when it switches to petrol, and also what you've said about the vapouriser temperature, I'd say it's switching back because the vapouriser temperature is too low.

Why this relates to tank level I really can't explain, but every vapouriser I've seen has been too hot to touch when the engine is running and fully hot. It has a coolant jacket around it so it's bound to be if the flow is good. Condensation on it is certainly not right.

From the behaviour of the LED when it switches to petrol, and also what you've said about the vapouriser temperature, I'd say it's switching back because the vapouriser temperature is too low.

Why this relates to tank level I really can't explain, but every vapouriser I've seen has been too hot to touch when the engine is running and fully hot. It has a coolant jacket around it so it's bound to be if the flow is good. Condensation on it is certainly not right.

I still think it's a coolant flow issue around the vapouriser.

Agreed, thanks, I think were both kind off on the same page with this one and the Vap temperature, which is always good to know, Im currently doing another flush, hopefully this weekend so lets see if it improves even further, if it does but not quiet cures it, then maybe a bit more with the Vap and heater matrix and some reverse fushing and check hose flow etc, otherwise a Vap strip down could be in order which Im trying to avoid if poss.

I want try and nail this before the warmer weather hits us, as Ive got a strange feeling this may temporary cure itself only to reappear next winter otherwise.

Just wondering if coolant circulation in general is marginal - broken impeller in the water pump, perhaps?

Also might be worth checking it's not plumbed into the heater matrix bypass path or something. I know it's a "factory LPG" setup, but who knows?

Heating works ok, gets hot, could do with getting hotter if I compare with a 1.6 Tigra (that gets piping hot on full blast) thats all Ive got close enough to compare with never had a Corsa.

Water pump, looks brand New, obviously been changed recently, no idea for what reason.

Ive change the Thermostat, wasn't convinced it was that, but 5 min job would be rude not to, no difference.

I did have a quick look at the HBV for that reason, couldn't find it, may be its tucked out of the way as are some of the Hoses, but the Vap is definitely in parallel to the Heater Matrix, as said before was thinking of pumping the Vap in series before the heater but would rather leave as it come from the factory if Im honest.

Yep, you'd hope the factory configuration would work. Many cars (especially without air con) just put the flow through the matrix 100% of the time and blank it off with the air flaps when "cold" is selected, so there may not be a HBV.

Another possibility is that the run to the vapouriser is airlocked somehow so the flow is reduced.

I wonder if it's worth temporarily clamping one of the hoses to the heater matrix to see if that helps? It might help clear any airlock / blockage in the vapouriser circuit, or at least prove that we're onto something if it improves the running on LPG.

Yep, you'd hope the factory configuration would work. Many cars (especially without air con) just put the flow through the matrix 100% of the time and blank it off with the air flaps when "cold" is selected, so there may not be a HBV.

Another possibility is that the run to the vapouriser is airlocked somehow so the flow is reduced.

I wonder if it's worth temporarily clamping one of the hoses to the heater matrix to see if that helps? It might help clear any airlock / blockage in the vapouriser circuit, or at least prove that we're onto something if it improves the running on LPG.

Clamp the heater hose before matrix, I like that one, will try that, as you say may force any crap or air out through the Vap.

Im in it tommorow on a trip to London, so just for you Kevin I will freeze my nuts off for the Day and if my fingers still work in the Evening report back

Just thinking back to an earlier 2.5 conversion done by a certain Army Medic...

Was about to say all the Vx Dual Fuels Ive come across are Spare Wheel mounted, except this one its a Cylinder behind the front seats, well I assume its cylinder as its encapsulated in a custom made steel case, I can rip it apart and have a look, how should the Cylinder be mounted position wise?